Pin-hole leaks from a fire-control sprinkler piping system just above the false ceiling of multiple rooms in an office building resulted in a suit against three parties involved with supplying the system. The plaintiff - a financial service organization that owned the building - had much computerized transaction data stored on magnetic tapes in several rooms damaged or destroyed by the incident. The monetary loss was major. The leaks occurred within two years after the system was installed. This period is clearly far short of the expected life of the system. Defendants in the case included the supplier of the piping used in the system, the engineering firm that designed it and the installation contractor.

I assisted the attorney representing the installation contractor as an engineering expert witness in the areas of mechanical and corrosion engineering. It appeared that corrosion was a likely cause of the failure. A written report plus my deposition were provided.

Each defendant had at least one engineering expert assisting them. It was soon confirmed that the galvanized steel material used for the piping was not at fault and the system design met standards without deficiencies. However, it was clear that the piping had leaked because of corrosion but it was unclear what the installation contractor did that produced the attack. Further it was initially unclear what type of corrosion was involved. The latter question soon became important.

This was a dry, or pre-action, type of sprinkler system that is widely used. This system was filled with pressurized air under the normal, i.e., the "no fire", condition and not continually filled with water as in a "wet" system. Heat sensors in a dry system send signals to an upstream, normally closed automatic, pre-action valve in the water supply piping to open and flood the sprinkler system when a fire condition is detected. Water is then discharged through pendent type sprinkler heads mounted below the false ceiling when they open at a pre-set temperature.

A near-final step in the system's installation sequence is to pressure test (hydro test) all the piping with raised pressure water to assure the integrity of the system's mechanically fastened joints. When the pipe joints are secure, the hydro test water is completely drained out of the sprinkler piping through multiple drain valves.

This system was a fire-safety approved, level design type (not sloped) so that water used in the hydro test was intended to be completely drained using several drain valves located at specified intervals. The installation contractor completed placement and joints of all the level piping, pendent valves and all required drain valves as designed but there was a period after this work before he could complete the hydro test and system drainage. In the construction industry it is not unusual to have certain tasks completed, followed by a period of inactivity and, finally, to finish remaining tasks within the contracted period. That sequence was followed here.

Internal inspections of the pipe sections showed they contained medium to significant quantities of water and dark, flat gel-like deposits that covered pin-holes in the bottom of the pipe. A dark gel-like substance is often characteristic of microbiological influenced corrosion (MIC) in steel pipe. Small, conical shaped deposits were also found in several of the affected pipe sections. These are known as tubercles. During MIC specific bacterium grow in certain waters and form a gel-like deposit (called a biofilm) and sometimes tubercles on a metal surface. MIC growth is more rapid in stagnant water conditions. The presence of these two types of deposits produce corrosion that often looks like pitting under the deposits but the root-cause mechanism is not pitting. In this case samples of the biofilms were collected from different pipe locations and sent to a specialized laboratory for analysis. That procedure consisted of comparing the DNA of the bacteria in collected samples to a database of DNA of various bacteria that are known to cause MIC. The results showed that MIC was indeed the most probable cause of this corrosion within a reasonable degree of engineering certainty.

The finding of MIC was unfortunate for the building's owner because his liability insurance did not cover damage due to MIC. This was because at the time of this case MIC was not as widely known as today and it was not included in some insurance contracts. However, at first the owner was not concerned due to the fact that inspection showed water in the piping that should not have been present if proper drainage had been accomplished by the installation contractor. Thus initially it appeared the installation contractor was at fault and would have full liability for the damage.

Several types of construction work occurred during the time the sprinkler system was being installed. After checking the work schedules of all the different contractors in the building and final inspections completed by the building owner's representatives, it was found that the sprinkler installation contractor was not responsible for the MIC. It was confirmed that an electrical contractor worked above false ceilings after the sprinkler contractor had completed his initial level piping placement work but before he did the hydro test and draining. The electrical contractor moved the sprinkler piping in order to simplify wiring installation. When that contractor moved the formerly level pipe low points were created. Not all water used in the hydro test could then be released through the correctly placed drained valves. Those low areas retained stagnant water that promoted MIC. The case against the sprinkler installation contractor was dropped.

Gerald O. Davis, PE, President and co-owner of DM&ME, has over 40 years experience in Materials Engineering and Business. Mr. Davis is a Forensic Expert in Materials Usage, Corrosion, Metallurgy, Mechanical Failure, & Root-Cause Failure Analysis. His recent background includes work as a corrosion researcher, senior engineer, and program manager for Battelle Memorial Institute, DNV, Inc., Henkels & McCoy, Inc., respectively and, since 2004, as president of DM&ME.